Phase manipulation and its applications in microwave circuits

Abstract

The wireless industry has been boosted over the decades. A lot of wireless applications are shifting to the higher frequency bands, which make the phase of a microwave signal more significant for the proper application of the whole circuits. Hence, it is valuable to investigate the issues of the phase manipulation in some of the microwave circuits such as antenna, active and passive components. This dissertation investigates three phase techniques namely the phase conjugation, phase inversion and phase combination/cancellation. By using these approaches of the phase manipulation effectively, some novel wideband or dual-band circuits are accomplished. An antenna array and some microwave components such as power divider, wideband bandpass filter and the dual-band bandstop filter are then proposed and analyzed in details. To begin with, a 2-dimensional phase-conjugating retrodirective array using the star-shaped antenna element is proposed. This 2-D cross-shaped antenna array which employed the low-conversion loss phase-conjugating mixer is able to achieve a good retrodirectivity with wide scan range of 120°. Our proposed dual-fed star-shaped antenna element is proposed for lowering the mutual coupling between the antenna elements. Furthermore, the antenna array is able to support the linear or circular polarization signals and the information carrying capability is demonstrated experimentally as well. Secondly, the phase inversion technique is used to implement two circuits. One is a two-way power divider with very wide isolation bandwidth and the other is a new type of wideband bandpass filter with a flat group delay. In the proposed power divider, the 20-dB isolation bandwidth is more than 160%. Experimental results also show that the fractional bandwidths are more than 50%, on the conditions of 20 dB return loss, less than 3.3 dB insertion loss (3 dB for ideal coupling) and 3° phase imbalance. As for the proposed wideband bandpass filter, the measured fractional passband bandwidth is 123% with a flat group delay response. Furthermore, over 90% impedance bandwidth is obtained for the return loss higher than 20 dB. The theoretical simulation, electromagnetic simulation, and measured results all show good agreement with this proposed design. Finally, a simple non-resonating dual-band bandstop filter using the technique of phase combination/cancellation is proposed. A prototype is demonstrated for eliminating the 2.4/5.8-GHz ISM applications. The measured results indicate that the dual fractional stopband bandwidths with 20-dB signal attenuation are 25.2% and 12.4%. Also, the theoretical simulation, electromagnetic simulation and measured results all show good agreement with this simple design. This design concept can also be easily applied to further implementation of the millimeter-wave filter by the same design flow. Detailed information for finding the exact transmission poles and zeros are discussed in this section.